1. Field of the Invention
The present invention relates to a driver circuit that drives a light emitting thyristor array, a driver apparatus that employs the driver circuit, a print head that employs the driver apparatus, and an image forming apparatus that employs the print head.
2. Description of the Related Art
Some electrophotographic image forming apparatus include an exposing section incorporating a plurality of light emitting thyristors as light emitting elements. A single driver circuit drives one or more light emitting thyristors. Each light emitting thyristor is energized by a trigger signal applied to its gate electrode, so that current flows from anode to cathode to emit light.
Japanese Patent Publication No. 2004-195796 discloses a self-scanned print head that incorporates light emitting thyristors. The self-scanned print head includes a scanning circuit in which a plurality of thyristors form a scanning circuit in the form of a shift register, and a plurality of light emitting thyristors emit light. The scanning circuit section specifies the order in which the light emitting thyristors are energized to emit light.
Conventional self-scanned print heads suffer from the following drawbacks. The light emitting thyristors have commonly connected anodes and commonly connected cathodes. Thus, the parasitic capacitances between the anode and cathode of the light emitting thyristors are connected in parallel with one another to form a large capacitance. When the light emitting thyristors are driven in sequence, the large capacitance causes a long delay time for each light emitting thyristor to emit light, shortening the time period during which the light emitting thyristor emits light. This is detrimental to the high speed operation of the print head, resulting in longer printing time.
There exists a need for the configuration that is effective in shortening the rise time that would otherwise tend to be long due to the parasitic capacitance of light emitting thyristors.